Lamps such as High Pressure Sodium (HPS) lamps, which are employed to enhance the growth of plants, may exhibit various limits and drawbacks.
For example, plants are able to absorb only a small fraction of the light spectrum of such lamps.
Moreover, some lamps emit UV radiation which, if not properly filtered, may be harmful both to plants and to operators e.g. in a greenhouse.
In addition, some lamps may contain metals harmful to the environment, and moreover they may be fragile and have a short operating life.
LED sources may be a valid solution to replace such traditional light sources, e.g. because they have a high-intensity light emission in a wavelength range adapted to foster plant growth.
Moreover, the possibility is given to use LEDs with different light emission features, so as to influence the overall spectral features of the emitted radiation.
The possible use of LED light radiation sources for plant lighting, e.g. in the horticultural sector, is the object of various patents.
For example, patent KR 100879711 describes a mixing of radiations produced by LEDs in the ranges of 640 to 675 nm and 425 to 455 nm, with different ratios: 9:1, 8:2, 7:3 and 6:4.
U.S. Pat. No. 6,921,182 B2 describes the use of orange, red and blue LED sets having different output angles.
U.S. Pat. No. 8,944,631 B2 describes a LED lighting unit of a mixed type, employing various units with red and blue LEDs. Each unit comprises three blue LEDs in a triangle, and eight red LEDs in four sets, which are arranged in a rectangular configuration.
U.S. Pat. No. 5,660,461 A describes a module comprising one or more U-shaped substrates, one substrate acting as a heatsink, and a cone-shaped reflector, being aligned so that the LED is located at the centre of the cone, the device comprising a plurality of modular units that are snapped together.
U.S. Pat. No. 6,042,250 A discloses a reflector having a plurality of flutes, adapted to reflect the light emitted by a source arranged at the focal point of the reflector, so as to obtain a uniform distribution of the radiation. The reflector is adapted to operate with various kinds of sources without jeopardizing the uniformity or the desired level of lighting in an area where plants are grown.
U.S. Pat. No. 8,174,688 B2 discloses a method for determining the number of different light sources provided in a lighting device having different RGB ratios.